Hydroelectric utility has to control with the flow

Located in an environmentally sensitive area, Box Canyon Dam has to deliver power while remaining invisible to the surrounding community. This means trying to control output around changes in water flow.

Jason Wright

01/10/2013

Box Canyon Dam, north of Spokane, Wash., was turning river current into electrical current long before renewable energy became an environmental hot topic. Since 1956, Box Canyon Dam and its four hydroelectric turbine-generator sets have straddled a narrow section of Washington state’s second-largest river, the Pend Oreille.

The Pend Oreille County Public Utility District built and operates the 80 MW hydroelectric plant, which today provides power to 8,500 customers. Most major hydroelectric plants generate electricity by systematically controlling the release of stored water behind a dam. However, Box Canyon is a run-of-the-river hydro plant, meaning the flow of water from upstream sources drives the submerged turbines without a retention area to help smooth out changes in flow. This means operators at Box Canyon have to maintain the delicate balance between optimal power generation and the river’s natural ecosystem.

Seasonal rains, melting snowpack, and other natural forces put pressure on Box Canyon, swelling the incoming flow from upstream dams and reservoirs. Swift currents are naturally a plus for hydro power production because more water provides more energy to turn the turbines. But state-protected lands behind Box Canyon can’t be allowed to flood because they’re home to sensitive animal habitat and picturesque public parks that attract thousands of visitors annually to Washington’s northeast corner. Consequently, Box Canyon operators work continuously, mostly by hand, to control the amount of water flowing through the dam and the elevation of the river behind it.

Challenges of an aging facility

Most of the original mechanical controls and hydroelectric equipment—including the four turbines, generators, and auxiliary machinery—remained much the same as when they were installed more than 50 years ago. “Even for a team of highly experienced operators, that’s a lot of working parts to monitor and adjust separately,” said Terry Borden, manager of hydro production at Box Canyon. “We also have to contend with whatever the weather throws at us.”

While the average flow rate at Box Canyon is 26,400 cfs (cubic feet per second), spring thaws and early summer rains can push that level to 80,000 cfs and above. At those rare heights, operators stop the turbines and open the dam’s hydraulic gates to let the river flow unfettered through spillways.

Day-to-day fluctuations in the river are far less dramatic, but still can vary significantly. To contend with those variations, operators constantly monitor flow rates and water elevations behind the dam. They use that information to control the flow through the dam by adjusting the turbines’ wicket gates, the large doors that open to allow water into the turbines. The goal is to keep power production as close to maximum as possible while keeping river levels as stable as possible.

Collecting critical data involved in the power generation process has also been a largely manual process, with operators recording instrument readings by hand. Without an electronic network to share the data, operators had to enter it into Excel spreadsheets and then distribute hard copies to other departments. Purchasing employees, for example, use month-to-month trending data to help calculate power contracts.

“All our systems were out of date,” Borden said. “And because no real upgrade of the control station and the equipment had been done since the plant was built, everything was just worn out.”

Regulators want more

The Federal Energy Regulatory Commission (FERC) recently noted the need for modernization when Box Canyon applied to renew its license for the next half century. FERC granted the license but stipulated the plant had to invest in upgrades to comply with the latest federal standards. “We needed state-of-the art automation to meet all our requirements, from integrated control to real-time reporting to plant security,” Borden said.

Before the project began, Borden and his team planned on approaching Rockwell Automation to provide the comprehensive control solution the plant needed. Borden notes, “We had invested in four Allen-Bradley SLC controllers, one on each turbine’s governor blade control system, so we had some experience with Rockwell Automation.”

The Pend Oreille utility district selected the PlantPAx process automation system, an integrated control and information solution that combines capabilities of a distributed control system with access to process information to help achieve plant-wide optimization. Implementation of the PlantPAx solution at Box Canyon is happening in stages, along with the rest of the $150 million project. The district must continue to produce power during the upgrade, using three of the four turbine-generator units at all times. One unit has already been replaced and the second is under way.

The process includes disassembling the unit down to its concrete foundation. Then the new turbine and generator are installed, along with new switch gear, relay-protection systems, pumps, and pipes.

The PlantPAx solution includes two Allen-Bradley ControlLogix PACs (programmable automation controllers) for each unit. One controls the turbine governor system and the other handles general unit controls, auxiliary pumps, and stopping and starting the generators. In the control room, a series of FactoryTalk View supervisory edition HMIs provide operators with valuable information and diagnostics via EtherNet/IP. FactoryTalk SE Server software consolidates HMI data from the hydro units, allowing Box Canyon operators to monitor and manage system parameters, such as river elevations and flow rates, from a central point. FactoryTalk Historian SE provides for centralized data, event, and alarm databases.

“The PlantPAx system architecture also opens up communication between the PACs and third-party equipment through EtherNet/IP, so valuable information is instantly available to everybody who needs it,” Borden said.

Results

The new system has helped increase generating efficiency at the plant by allowing more exact monitoring of the turbine and generator systems. In turn, operators can detect and correct problems earlier, such as high temperatures in the generator or low flow in cooling systems.

“It’s too soon to put a number on it, but we anticipate this increased reliability and unit uptime will reduce operating costs once the entire project is complete,” Borden said. “Operators will also be able to perform additional maintenance tasks they don’t have time for now, like digging trash out of the intakes. The ControlLogix controller and FactoryTalk software have allowed us to capture more real-time information, and retain it for future analysis and trending. System data is also automatically sent to a corporate network database that allows other departments to easily access the information, rather than shuffle through print-outs.”

The security features offered by the FactoryTalk Asset Centre software also enable the direct reporting and documentation required under the NERC CIP (North American Electric Reliability Corporation’s critical infrastructure protection) provisions. Once the turbine-generator project is completed, Borden and his team plan to take full advantage of the remote monitoring capabilities offered by the new process control system. The utility district operates a smaller dam and pumping stations outside Box Canyon, and it plans to improve their connection to the district’s SCADA system.

“Our new process capabilities will allow the district to monitor and operate remote sites from one central location, saving on both labor and travel costs,” Borden said.

Also on the utility’s agenda is another installation important to Oregonians: adding a fish passage system at the dam. This will protect bull trout and other species on their downstream and upstream journeys.